The subject matter of the present invention relates generally to electron image storage apparatus, and in particular high resolution scan conversion type storage tubes and the method of erasure of such tubes.
In conventional charge storage scan conversion tubes, it has been a common practice to employ a single electron gun to perform the necessary writing, reading, and erasure functions of the dielectric target structure therein. Such operation is facilitated by well-known techniques, such as proper manipulation of electron beam current and target backplate voltages for the various functions.
In high resolution scan conversion systems, and particularly in focus projection and scanning electron beam systems where small tube size and low power consumption are essential, an extremely narrow electron beam is required to provide the fine spot of this beam on the target for writing and reading. Such a narrow beam is usually ensured by providing a disk portion of the electron gun with a very small aperture for passage therethrough of the electron beam. However, while the small aperture defines the radial extent of the beam, it unfortunately also limits the beam current, and thus erasure of the storage dielectric is severely affected. Hitherto, erasure has been accomplished by scanning the target many times using the reading beam to remove the charge. Consequently, the time required for complete erasure is considerable and the usefulness of the device is thereby limited.